In pneumatic brake systems, air is typically supplied by an air compressor. The compressed air is usually passed through an air dryer to remove moisture from the air which might adversely affect performance and longevity of the system. Under normal conditions, the temperature of air leaving the compressor is typically between 200-350.degree. F. The standard maximum recommended air input temperature for air dryers, however, is 150.degree.-160.degree. F. As such, aftercoolers have sometimes been interposed between compressors and dryers to reduce the temperature of air leaving the compressor to a level acceptable for input to an air dryer. A disadvantage of aftercoolers, though, is that in extremely cold environments they may disadvantageously reduce the temperature of air entering the dryer to below 32.degree. F. such that any moisture in the air may freeze and clog the dryer, adversely affecting system operation.
U.S. Pat. No. 3,841,064 to Hitchiner et al. discloses an aftercooler having a condensate discharge valve built into the bottom thereof so as to be heated by the air from the compressor. The typically warm air leaving the compressor inhibits condensate from freezing within the aftercooler discharge valve, thereby inhibiting clogging. A disadvantage of this design, however, is that clogging of the air dryer by freezing condensate may still occur.
U.S. Pat. No. 4,237,696 to Coblentz discloses a compressed air system having a bypass/repass valve to bypass or repass the heat exchanger coils when the temperature reaches a predetermined level. The valve, which is positioned before the compressor, can be manually manipulated or operated automatically through a thermostat connected by wiring to a damper motor connected by a standard damper linkage to the valve. A disadvantage of this prior art design is that the bypass valve is designed to operate in conjunction with a cooler and dryer unit located before the air compressor. Thus, heating which occurs within the compressor itself necessitates the provision of a second cooler and dryer unit located after the compressor, thereby increasing the cost of the compressed air system. Another disadvantage of this prior art design is that the bypass/repass valve system is complex, including electromagnetic components, such as a damper motor. As such, the system is costly to produce and prone to mechanical failure.
What is desired, therefore, is an air aftercooler for a pneumatic brake system which inhibits clogging of the air dryer by freezing condensate, which is capable of being located in the brake system downstream of the compressor and which is reliable and not prone to mechanical failure.